Pyridine dicarboxylic ester metal extractants

ABSTRACT

Metal values are extracted from aqueous solutions of metal salts containing halide or pseudo halide ions by pyridine derivatives containing the substituent --(COX) A  where X is the group --OR 1  or --NR 2  R 3  and n is 1, 2 or 3. R 1  is a hydrocarbyl group containing from 5 to 36 carbon atoms and R 2  and R 3  are hydrogen or a hydrocarbyl group wherein R 2  and R 3  together contain from 5 to 36 carbon atoms. The process is especially useful for the recovery of metals from leach solutions derived from sulphur-containing ores such as chalcopyrite.

This is a division of application Ser. No. 418,833, filed Sept. 16,1982, now U.S. Pat No. 4,525,330 which in turn is a continuation-in-partof application Ser. No. 341,176, filed Jan. 20, 1982, now abandoned

This invention relates to a process for the extraction of metal valuesfrom aqueous solutions of metal salts, and in particular to a processfor the extraction of metal values from aqueous solutions in thepresence of halide anions.

The use of solvent extraction techniques for the hydrometallurgicalrecovery of metal values from metal ores has been practised commerciallyfor a number of years. For example copper may be recovered from oxideores or from ore tailings by treating the crushed ore with sulphuricacid to give an aqueous solution of copper sulphate which issubsequently contacted with a solution in a water-immiscible organicsolvent of a metal extractant whereby the copper values are selectivelyextracted into the organic solvent phase.

The application of solvent extraction techniques to aqueous solutionscontaining halide ions however has hitherto presented numerous technicalproblems.

Of particular importance in this connection is the development ofhydrometallurgical routes (as an alternative of smelting) for theextraction of metal values from sulphur-containing ores such aschalcopyrite. Such ores may be leached for example using ferric chlorideor cupric chloride solutions, but the solvent extraction of theresultant leach solution presents formidable difficulties.

The present invention provides a process for the extraction of metalvalues from aqueous solutions containing halide ions by the use of metalextractants whose several properties meet the stringent requirementsimposed on the extractant by the system.

According to the present invention there is provided a process forextracting metal values from aqueous solutions of metal salts containinghalide or pseudo halide anion which comprises contacting the aqueoussolution with a solution in a water-immiscible organic solvent of asubstituted pyridine of formula: ##STR1## wherein X is the group --OR₁or --NR₂ R₃, R₁ being a hydrocarbyl group containing from 5 to 36 carbonatoms and R₂ and R₃ being hydrogen or a hydrocarbyl group, R₂ and R₃together containing from 5 to 36 carbon atoms, and n is 1, 2 or 3.

When n is 2 or 3, the substituent --X in the respective groups --COX maybe the same or different. For example, when n is 2, the two groups --COXmay be --COR₁ and --COR₁ ' respectively where R₁ and R₁ ' are bothhydrocarbyl groups containing from 5 to 36 carbon atoms. Similarly, whenn is 2, the two groups --COX may be --COR₁ and --CONR₂ R₃ respectively.

According to a further aspect of the present invention there is provideda process for extracting metal values from aqueous solutions of metalsalts containing halide or pseudo halide anion which comprisescontacting the aqueous solution with a solution in a water-immiscibleorganic solvent of a 3- or 4-substituted pyridine of formula: ##STR2##wherein X is the group --OR₁ or --NR₂ R₃, R₁ being a hydrocarbyl groupcontaining from 5 to 36 carbon atoms and R₂ and R₃ being hydrogen or ahydrocarbyl group, R₂ and R₃ together containing from 5 to 20 carbonatoms.

According to a further aspect of the present invention there is providednovel metal extractants. Thus there is provided a 3- or 4-substitutedpyridine of formula ##STR3## wherein X is the group --OR₁ or --NR₂ R₃,R₁ being an alkyl group containing from 9 to 24 carbon atoms and havingthe formula ##STR4## wherein R₄ and R₅ are alkyl groups, and R₄ containstwo fewer carbon atoms than R₅, and R₂ and R₃ together containing atotal of from 15 to 36 carbon atoms, provided that when R₂ is hydrogen,R₃ is a branched chain alkyl group.

There is also provided a substituted pyridine of formula: ##STR5##wherein X is the group --OR₁ or --NR₂ R₃, and n is 2 or 3, therespective groups R₁ being alkyl groups containing a total of from 16 to36 carbon atoms, and the respective groups R₂ and R₃ being alkyl groupswherein the total number of alkyl carbon atoms contained in all therespective groups R₂ and R₃ is from 20 to 70.

The pyridine ring may carry substituents in addition to the group(s)--COX. Examples of suitable substituents are halogen groups, alkylgroups, aryl groups, alkoxy groups, aryloxy groups, aralkyl groups,cyano groups and nitro groups. The pyridine ring may also carry acarboxylic acid group, and the invention includes for example a halfester of a pyridine dicarboxylic acid.

Substitution in the pyridine ring may for example result from the methodof synthesis. For example bis ester of 4-phenylpyridine-3,5-dicarboxylicacid may be prepared from methyl propiolate, aromatic aldehydes andammonium acetate in acetic acid followed by oxidation to the pyridinederivative and ester exchange (Chennat and Eisner, J. C. S. Perkin I,1975).

When n is 1, examples of compounds which may be used in the process ofthe invention include esters or amides of nicotinic acids, isonicotinicacids and picolinic acids. When n is 2, examples of compounds which maybe used in the process of the present invention include bis esters oramides of pyridine-2,4-dicarboxylic acid, of pyridine-2,5-dicarboxylicacid, and of pyridine-3,5-dicarboxylic acid. When n is 3, examples ofcompounds which may be used in the process of the present inventioninclude tris esters or amides of pyridine-2,4,6-tricarboxylic acid.Mixtures of such compounds may be used, for example a mixture of bisesters or amides of isomeric pyridine-dicarboxylic acids.

The substituted pyridines of the present invention wherein X is thegroup --OR₁ may be prepared by conventional means, for example by thereaction of a pyridine carboxylic acid, for example isonicotinic acids,nicotinic acids or picolinic acids respectively with the appropriatealcohol to form the desired esters. Alternatively the lower esters, forexample methyl or ethyl esters may be subjected to ester exchangereactions with higher alcohols, or the acid chlorides may be reactedwith the appropriate alcohol or phenol. Dicarboxylic acid esters ofpyridine may conveniently be prepared from lutidines, for example byoxidation and esterification.

R₁ may for example be an alkyl group, for example an octyl, nonyl,decyl, dodecyl, tridecyl, pentadecyl, hexadecyl or octadecyl group orsubstituted alkyl group, for example a group containing one or morepropylene oxide residues formed by reacting propylene oxide with analcohol before esterification to give the substituted pyridine; R₁ maybe a cyclo alkyl group such as cyclohexyl; R₁ may be an aralkyl groupsuch as benzyl; or R₁ may be an aryl, alkylaryl or alkoxyaryl group forexample p-nonylphenyl or p-dodecylphenyl.

When n is 1 and there is no other substituents in the pyridine ring, R₁is preferably a branched chain alkyl group containing from 9 to 24carbon atoms.

R₁ may be an isomeric mixture of groups containing the same number ofcarbon atoms or a mixture of groups containing different numbers ofcarbon atoms (which may themselves be an isomeric mixture), for examplea mixture of different alkyl groups, If R₁ is a mixture of groupscontaining different numbers of carbon atoms, the average number ofcarbon atoms is preferably from 9 to 24.

Highly branched groups R₁ may usefully be obtained by the reaction ofthe pyridine carboxylic acid with alcohols prepared by the Guerbet andAldol condensations. Such alcohols are characterised by branching at theposition beta to the hydroxyl group, and have the general formula:##STR6## In general R₄ contains 2 fewer carbon atoms than R₅, and groupsR₁ derived from these alcohols include for example, ##STR7## R₄ and R₅may be straight chain or branched chain alkyl groups and may be isomericmixtures of alkyl groups. A mixture of highly branched alcohols may beobtained by Guerbet or Aldol condensations of mixtures of alcohols andaldehydes respectively.

Excellent solubility is conferred upon the compounds of formula I wherethe alcohol is the product of the aldol dimerisation of commercialnonaldehyde. In this alcohol the group R₁ is believed to consistessentially of a mixture of geometrical isomers of a radical of theformula: ##STR8##

When n is 2, the respective groups R₁ (R₁ and R₁ ') may be any of thosegroups R₁ listed previously. R₁ and R₁ ' are conveniently the same andare preferably straight chain or branched chain alkyl groups. When n is2, we have found that to achieve the desired solubility of the metalcomplex in preferred solvents, R₁ and R₁ ' preferably together contain atotal of from 16 to 36 carbon atoms. The groups R₁ may contain a mixtureof isomers, for example a mixture of nonyl isomers derived fromisononanol obtained by the hydroformylation of a mixture of octenes, amixture of decyl isomers obtained from isodecanol, or a mixture oftridecyl isomers obtained from tridecanol.

The substituted pyridines of the present invention wherein X is thegroup --NR₂ R₃ may be prepared by conventional means, for example byreaction of pyridine carboxylic acids and their lower esters with higherprimary or secondary amines. Alternatively the acid chloride of thepyridine carboxylic acid may be reacted with the appropriate amine.

The amide group --NR₂ R₃ may be primary (R₂ is hydrogen) or secondary.R₂ and R₃, which may be the same or different may be groups of the typeindicated above for R₁. R₂ and R₃ taken together contain from 5 to 36carbon atoms. Thus R₂ may be for example a lower alkyl group, forexample a methyl group, provided R₃ is correspondingly larger. R₂ l andR₃ taken together are preferably alkyl groups containing a total of 15to 36 carbon atoms. For secondary amides sufficient solubility inpreferred organic solvents may generally be achieved if R₂ and R₃ arestraight chain or branched chain alkyl groups. However for primaryamides (R₂ is hydrogen), R₃ is preferably a branched chain alkyl group.When n is 2, and the groups R₂ and R₃ l are all alkyl groups, the totalnumber of alkyl carbon atoms preferably does not exceed 70, for examplethe total number of alkyl carbon atoms is preferably from 20 to 70.

The process of the present invention may be applied to the extractionfrom aqueous solutions containing halide or pseudohalide ion of anymetal capable of forming a stable halide- or pseudohalide-containingcomplex with the pyridine derivative in the water-immiscible organicsolvent. Examples of such metals include copper, cobalt, cadmium andzinc. The process of the present invention is especially applicable tothe solvent extraction of copper from aqueous solutions obtained by thehalide or pseudo halide leaching of sulphur-containing copper ores, forexample from solutions obtained by the leaching of ores such aschalcopyrite with aqueous ferric chloride or cupric chloride solutions.

The leaching of ores such as complex sulphide ores, for examplechalcopyrite with for example aqueous ferric chloride solutioncontaining hydrochloric acid gives rise to leach solutions containingcuprous and cupric ions, ferrous and ferric ions and excess chlorideanion. The ratio fo cuprous to cupric ion depends on the leachconditions selected. The sulphur content of the ore may be precipitatedas elemental sulphur. Whilst the scope of the present invention is notto be taken as being limited to the treatment of any particularhalide-containing aqueous solution, typical solutions obtained by theleaching of chalcopyrite with acidified ferric chloride may containbetween 10 and 60 grams per liter of copper, between 50 and 150 gramsper liter of iron, may typically be between 0.1M and 1M hydrochloricacid and may be between about 2M and 8M in total chloride ion. Certainleach systems may give total chloride ion contents as high as 10M or12M. All leach solutions encountered in practice will also containvarying quantities of the many other metals present in the ore body.Certain leach solutions may contain high levels o specific metals, forexample zinc, in addition to copper. copper.

It will be appreciated that the process of the present invention may beincorporated into a wide variety of different methods for the overallrecovery of metals from their ores or from other metal-bearing sources.Details of these methods will vary depending on the metal concerned andthe nature and composition of the leach solution. Whilst the process ofthe present invention is not limited to any single overall method forthe recovery of metals, the stringent conditions imposed on the pyridineextractant are best illustrated if the solvent extraction process isseen as a step in an integrated process of the recovery of the metalfrom the ore. For example an integrated process which is especiallysuitable for leach solutions containing high level of cupric ioncomprises the following steps:

1. Leaching of the ore with aqueous ferric or cupric chloride solutions,and removing the elemental sulphur produced;

2. Contacting the leach solution from step 1 (in which the ferric ion isat least partially reduced to ferrous ion) with a solution in awater-immiscible solvent of the extractant, whereby the copper istransferred into the organic phase in the form of a chloride-containingcomplex with the extractant;

3. Separating the organic phase containing the complex of copper withthe extractant from the aqueous phase containing the ferric/ferrouschloride;

4. Contacting the organic phase from step 3 with an aqueous stripsolution which is water, or which contains a reduced concentration ofchloride ion, whereby the chloride-containing complex of copper with theextractant is unstable and copper transfers into the aqueous stripsolution;

5. Separating the organic phase containing the stripped extractant fromthe aqueous strip solution containing the copper chloride; and

6. Electrolysing the strip solution from step 5 to recover copper. Theelectrolysis step is suitably arranged such that oxidation of ferrousion with transfer of chloride ion takes place in the anode compartment,such that the solution leaving the cathode compartment is denuded inboth copper and chloride ion. Alternatively chlorine gas may be evolvedat the anode and optionally used as oxidant to regenerate the leachsolution.

In order to preserve the overall stoichiometry of the sequence ofreactions, it may be necessary to provide additional oxidation offerrous to ferric ion, and to remove the iron entering the systemcontinuously from the chalcopyrite (CuFeS₂), for example in the form ofiron oxide such as geothite.

For a fully integrated process it is highly desirable that the solutionsbe re-circulated between the various stages. Thus aqueous strip solutionused in step 4 is preferably derived from the electrolysis step 6 and ispreferably the solution leaving the cathode compartment denuded in bothcopper and chloride ion. Similarly the organic phase containing thestripped extractant which is separated in step 5 is preferablyre-circulated to the extraction stage 2. The ferric chloride solutionderived from the electrolysis step 6 may be returned for furtherleaching of the ore.

Considering first the extraction stage 2 and the strip stage 4, theextraction of for example cupric ion by the extractant may berepresented by an equation such as the following:

    2L.sub.org +Cu.sup.++.sub.aq +2Cl.sup.-.sub.aq ⃡(L.sub.2 CuCl.sub.2).sub.org

This equation is a grossly oversimplified representation of a verycomplex process and is not to be taken as in any way limiting the scopeof the present invention, but it serves to illustrate the formation of aneutral organic phase complex of copper and the extractant (L) which isbelieved to predominate in the process of the present invention. Otherequations may be used to represent the extraction and stripping ofcuprous ion or of other metals by the extractant.

The above equation assumes that the extractant acts as a monodentateligand, and whilst this is believed to be generally true, esters andamides of 2-carboxypyridines do at least have the potential of acting asbidentate ligands. Under certain conditions other species, for exampleoligomeric complexes such as L₂ (CuCl₂)_(n) may be formed. The formationof oligomeric species is generally undesirable since the efficiency ofcopper extraction is reduced and in addition the oligomeric complexestend to have a low solubility in organic solvents. We have found thatthe tendency to the formation of oligomeric species is especially lowwith esters and amides of 2-carboxypyridines.

The equation also illustrates the reversible nature of the extraction,whereby the complex of copper and the extractant in the organic phasecan be stripped on contact with water or with an aqueous solutioncontaining a reduced chloride or a reduced copper content such thatcopper is transferred to the aqueous phase and the free extractant is atleast partially regenerated in the organic phase.

Most efficient stripping will be obtained using water itself as thestripping medium, and the process of the present invention may becombined with a water stripping stage. However, it will be noted that ina fully integrated process, it is preferred that the loaded extractantbe stripped with the solution derived from the electrolysis stage anddenuded in copper and chloride ion. In an extreme case, the aqueousphase may be entering the electrolytic cell containing about 40 or 50grams per liter copper and may leave it still containing as much as 30grams per liter copper or more. The requirement that the extractant willbe able to efficiently extract copper from the leach solution, whilst atthe same time be stripped by a solution containing relatively highlevels of copper is exacting. Preferred extractants for use in theprocess of the present invention are capable of being stripped by anaqueous solution containing relatively high levels of copper, forexample from 20 to 35 grams per liter of copper.

Since the leach solution contains high levels of iron, it is clearlyimportant that the extractant should have good selectivity for copperover iron. The extractants of the present invention have this property.Of particular importance in an integrated system, where the copper isrecovered by electrolysis of the pregnant aqueous strip solution, isselectivity for copper over silver and other minor extractableconstituents of the ore. The reason for this is that whilst metals suchas zinc and cadmium are more electronegative than copper and are notelectrodeposited with it, silver is both co-deposited with copper andfurthermore adversely affects the physical properties of the copper sothat an expensive electrorefining stage is required. Preferredextractants of the present invention have excellent selectivity forcopper over silver under appropriate operating conditions.

A yet further property which is of importance for an extractant in theprocess of the present invention is the absence of significantprotonation by the acidic leach liquor. Such protonation may berepresented by an equation such as:

    L.sub.org +H.sup.+.sub.aq +Cl.sup.-.sub.aq ⃡(LH.sup.+ Cl.sup.-).sub.org

where L is the extractant. Such protonation of the ligand not onlycarries hydrochloric acid into the organic phase, building upunnecessary chloride concentration on the strip side, but is alsobelieved to be associated with loss of selectivity for copper oversilver and other trace components such as antimony and arsenic. Againthe preferred extractants of the present invention have excellentresistance to protonation even in contact with relatively acidic leachsolutions.

As illustrated by the Examples, the extractants of the present inventionprovide a range of properties so that the optimum extractant may beselected for a given leach solution. In particular, a "strong"extractant, for example, isooctadecyl nicotinate, is capable ofextracting high levels of copper from a leach solution containingrelatively low chloride ion content (for example about 3.7M) but tendsto undergo undesirable protonation and acid transfer at higheracid/chloride ion concentrations (for example H⁺, 0.1M; Cl⁻, 9.8M). Onthe other hand, a "weak" extractant such as a diester ofpyridine-2,5-dicarboxylic acid is found to transfer only low levels ofacid, even from solutions concentrated in chloride ion and acid (forexample 10.7M and 1M respectively). Furthermore the lower inherentability of the extractant to transfer copper into the organic phase isoffset by the improved transfer of copper at these higher chloride ionconcentrations.

Bis esters of pyridine-3,5-dicarboxylic acids, for example the bis-nonylester, are weak extractants which furthermore show high selectivity forcopper over zinc, and provide a potential for recovery of zinc in leachsolutions containing high levels of both copper and zinc.

Examples of suitable water-immiscible organic solvents are aliphatic,aromatic and alicyclic hydrocarbons, chlorinated hydrocarbons such asperchloroethylene, trichloroethane and trichloroethylene. Mixtures ofsolvents may be used. Especially preferred in conventionalhydrometallurgical practice are mixed hydrocarbon solvents such as highboiling, high flash point, petroleum fractions (for example kerosene)with varying aromatic content. In general, hydrocarbon solvents having ahigh aromatic content, for example AROMASOL H which consists essentiallyof a mixture of trimethylbenzenes and is commercially available fromImperial Chemical Industries PLC (AROMASOL is a registered trade mark),provide a higher solubility for the extractant and its copper complex,whilst kerosene having a relatively low aromatic content, for exampleESCAID 100 which is a petroleum distillate comprising 20% aromatics,56.6% paraffins and 23.4% naphthenes commercially available from ESSO(ESCAID is a registered trade mark) may in certain cases improve thehydrometallurgical performance of the extractant. Factors influencingthe solubility of the extractant and its copper complex are complicated,but in general extractants having highly branched substituents and/or anisomeric mixture of substituents have comparatively high solubility.

We have found that isonicotinic acid derivatives and their coppercomplexes, for example (2-hexyldecyl)isonicotinate, have surprisinglyhigh solubility in both high and low aromatic content hydrocarbonsolvents.

The concentration of the extractant in the water-immiscible organicsolvent may be chosen to suit the particular leach solution to betreated. Typical values of extractant concentration in the organic phaseare between about 0.1 to 2 Molar, and an especially convenient range isfrom 0.2 to 0.8 Molar in the organic solvent.

The extraction stage and the strip stage of the solvent extractionprocess may conveniently take place at ambient temperature. However itis possible to improve net copper transfer from the leach solution tothe strip solution if the extraction stage is operated at ambienttemperature, whilst the strip stage is operated at elevated temperature,for example up to 50° C. We have also found that the undesirableformation and build-up of oligomeric complexes of the extractant andcopper may be alleviated if the strip stage is operated at elevatedtemperatures, for example up to 50° C.

The invention is illustrated by the following Examples in which allparts and percentages are by weight unless otherwise stated.

EXAMPLE 1

(2-(n)Hexyldecyl)nicotinate was prepared as follows:

A stirred mixture of nicotinic acid (61.5 parts), dimethylformamide(0.63 parts) and xylene (174 parts) was heated to 80° below a condenserset for reflux. Thionyl. chloride (65.5 parts) was then added during 1-2hours, the temperature of the reaction mixture being allowed to rise to90°-95° during the addition. The mixture was then stirred at 90°-95° for3 hours. The condenser was then set for distillation and the temperaturewas raised until excess thionyl chloride had distilled and xylene hadbegun to distil. The mixture was then allowed to cool to 80°-85° and2-(n)hexyldecanol (112 parts) was added during 30 minutes. The mixturewas stirred at 80°-85° for 2 hours and was then cooled to roomtemperature, and extracted with a solution of sodium hydroxide (40parts) in water (165 parts). The xylene solution was washed alkali freewith more water, and the xylene was distilled under reduced pressureleaving (2-hexyldecyl)nicotinate [147 parts] as a brown oil. The puritywas estimated at 95% by titration of a sample with N/10 perchloric acidin acetic acid medium. The compound was distilled, b.p. 176°-184° at 0.4mm pressure, yielding 109 parts of straw-coloured liquid which was98-99% pure.

The ability of (2-(n)hexyldecyl)nicotinate to extract copper fromaqueous solution containing chloride ion was investigated.

An aqueous solution (A) was made up which was 0.1M in cupric chloride(6.35 gpl copper), and 0.1M in hydrochloric acid, and which contained inaddition 250 g/liter of calcium chloride dihydrate. This solution wasthen agitated for 15 minutes with an equal volume of a solution (B)which was a 0.2M solution of (2-hexyldecyl)nicotinate in AROMASOL H. Thelayers were allowed to separate and settle, and were separately analysedfor copper content. The percentage of the copper initially present in Awhich had passed into B, was 44.5%. The resultant loaded organicsolution B was then stripped with an aqueous solution (C) which was0.472M in cupric chloride, i.e. one which contained 30 gpl of copper. Itwas found that copper passed from the organic to the aqueous solution.The percentage of the copper originally present in A which had beentransferred to solution C was 25.5%. The transfer of hydrochloric acidfrom solution A to soluion B was negligible.

Extraction of copper by the same extractant from a more strongly acidicsolution was also examined. The same solutions and procedure as beforewere used, except that solution A was 1.0M rather than 0.1M hydrochloricacid. The percentage of copper extracted into the organic solution (B)and the percentage which finally passed into the aqueous solution ofcupric chloride (C) were 47.8% and 30.6% respectively. The amount ofhydrochloric acid which passed from solution A to solution B under theseextremely acidic conditions was measured. Expressed as a percentage ofthat which would be transferred if every molecule of the ligand combinedwith one molecule of hydrochloric acid, the acid transfer was only 1.9%.

The above results are summarised in Table 1.

EXAMPLE 2

Tridecyl nicotinate was prepared using the method of Example 1 fromcommercial tridecanol (an isomeric mixture) and nicotinic acid. Theproduct had a boiling point of 136° to 140° C. under 0.05 mm pressureand an estimated purity of 100% based on a molecular weight of 305.5.

The ester was evaluated as an extractant for copper from aqueoussolution containing chloride ion using the method of Example 1.

The results are presented in Table 1.

EXAMPLE 3

N,N-di-(n)-octylnicotinamide was prepared using the method of Example 1from nicotinic acid and di-(n)-octylamine. The product had a boilingpoint of 180° to 183° C. at 0.15 mm pressure and an estimated purity of95.5%.

The amide was evaluated as an extractant for copper from aqueoussolution containing chloride ion using the method of Example 1.

The results are presented in Table 1.

It will be noted that this compound is a stronger extractant than thoseshown in the previous Examples, and would be more suitably employed forthe extraction and subsequent recovery of copper from an aqueoussolution of lower concentration of chloride ion. It would also bepreferable to strip the extractant with a strip solution which was lowerin copper and/or in chloride ion than solution C.

EXAMPLE 4

(2-(n)-hexydecyl)isonicotinate was prepared using the method of Example1 from isonicotinic acid and 2-hexyldecanol. The product had a boilingpoint of 180° to 190° C. at 0.75 mm pressure and an estimated purity of97.5%.

The ester was evaluated as an extractant for copper from aqueoussolution containing chloride ion using the method of Example 1.

The results are presented in Table 1.

                  TABLE 1                                                         ______________________________________                                                 Transfer of Transfer of Acid co-                                              copper (%)  copper (%)  extracted (%)                                         from 0.1 M HCl                                                                            from 1.0 M HCl                                                                            from 1.0 M HCl                               Extractant                                                                             to B    to C    to B  to C  to B                                     ______________________________________                                        Example 1                                                                              44.5    25.5    47.8  30.6  1.9                                      Example 2                                                                              44.6    26.2    47.6  29.8  3.3                                      Example 3                                                                              72.2    15.2    68.2  11.2  18.8                                     Example 4                                                                              51.0    23.8    57.0  31.4  3.0                                      ______________________________________                                         *For all Examples the acid coextracted from 0.1 M HCl to B was negligible                                                                              

EXAMPLE 5

A solvent extraction circuit was assembled consisting of small scalemixer settler units. The circuit comprised 3 stages of extraction and 2stages of stripping and pumping was arranged such that over both theextraction and stripping parts of the circuit the organic and aqueoussolutions flowed counter current wise.

The aqueous feed solution had the following composition of metals:

    ______________________________________                                        Copper (Cu.sup.2+) 16.0 g per liter                                           Iron (Fe.sup.2+)   40.4 g per liter                                           Silver (Ag.sup.+)  18.9 mg per liter                                          ______________________________________                                    

In addition, the solution contained 150 g per liter of calcium chlorideadded as the dihydrate CaCl₂.2H₂ O and contained 3.6 g per liter ofhydrochloric acid giving a total chloride ion concentration of 4.23moles per liter.

The strip solution consisted of an aqueous solution containing 28.9 gplcopper as cupric chloride with no added acid.

The solvent phase comprised a 19.2% by weight solution (0.553 moles perliter) of the extractant of Example 1 dissolved in AROMASOL H.

The pumps and agitators in the circuit were started and the flow ratesadjusted to give an organic flow of 33.3 ml/min and aqueous flows of13.3 ml/min (2.5 to 1 organic to aqueous phase ratio).

After the circuit had been running successfully for 4 working days at anaverage temperature of 15° C., samples taken from the aqueous raffinate;from the extraction circuit; and of the pregnant strip solution wereanalysed.

The results obtained are summarised in Table 2.

                  TABLE 2                                                         ______________________________________                                                                     Ag.sup.+                                                       Cu.sup.2+                                                                             Fe.sup.2+                                                                            mg/l                                                           gpl     gpl    (ppm)                                            ______________________________________                                        Aqueous feed    16.0      40.4   18.9                                         Raffinate       2.49      39.8   18.4                                         Strip solution  28.9      0.24   0                                            Pregnant strip solution                                                                       44.5      0.8    0.6                                          ______________________________________                                    

EXAMPLE 6

(2-(n)-Octyldodecyl)nicotinate was prepared from nicotinic acid and2-(n)octyldodecanol using the general method of Example 1 with thefollowing minor changes. The temperature after thionyl chloride additionwas maintained at 80° C. for 2 hours, and after the esterificationreaction, the solution was diluted with petroleum ether (60°-80° ),washed with water to remove acidity and the solvents removed bydistillation. The product had a boiling range of 190°-200° C. at 0.05 mmmercury pressure and an estimated purity of 87.9%.

The ability of (2-(n)octyldodecyl)nicotinate to extract copper fromaqueous solution containing chloride ion was investigated.

An aqueous solution (A) was made up which was 0.1M in cupric chloride(6.35 g/l copper), 0.1M in hydrochloric acid and contained 250 g/l ofcalcium chloride dihydrate, providing a total chloride ion concentrationof 3.7M. This solution was shaken for 1 minute with an equal volume of asolution (B) which was a 0.2M solution of (2-(n)-octyldodecyl)nicotinatein ESCAID 100. The layers were allowed to separate, the aqueous layerwas analysed for copper and the solvent layer for acid transferred withthe copper. The percentage of copper initially present in A which hadpassed into B was 52%. There was no detectable transfer of hydrochloricacid into B.

These results are summarised in Table 3.

EXAMPLE 7

Iso-hexadecyl nicotinate was prepared from nicotinic acid and acommercial material, iso-hexadecyl alcohol, obtained from FarbwerkeHoechst AG. The general method of Example 1 was used except that thetemperature after thionyl chloride addition was maintained at 80° C. for2 hours, and after the esterification reaction the solution was cooledand washed with 0.5M sodium hydroxide, 0.5M hydrochloric acid and water.The solution was treated with activated carbon (2.5 % on the expectedweight of product) at 50° C. for 1 hour, filtered and the solventremoved under reduced pressure. The light brown oil had an estimatedpurity of 93.4% and was distilled (boiling range 141°-146° C. at 0.03 mmmercury pressure) to provide a product of 99.8% estimated purity.

The ester was evaluated as an extractant for copper from aqueoussolution containing chloride ion using the method of Example 6.

To evaluate the efficiency of the extractant for use with leachsolutions containing higher level of total chloride ion, the generaltest method of Example 6 was repeated using a solution (A) whichcontained cupric chloride (0.1M), hydrochloric acid (0.1M) and 700 g/lcalcium chloride dihydrate, giving a total chloride ion concentration of9.8M.

The results are displayed in Table 3, and indicate that the extractantis more suitable for use with leach solutions having relatively lowtotal chloride ion concentrations (3.7M), since relatively acid transferlevels occur at high total chloride ion concentrations (9.8M).

EXAMPLE 8

Isooctadecyl nicotinate was prepared using the method of Example 7 fromnicotinic acid and a commercial product, isooctadecyl alcohol, obtainedfrom Farbwerke Hoechst AG. The product had an estimated purity 94.5%.

The isooctadecyl alcohol starting material was analysed by capiliary GasChromatography and gave traces showing four peaks each of which wasapproximately the same size. The commercial isooctadecyl alcohol isbelieved mainly to comprise different geometric isomer of2,2,4,8,10,10-hexamethyl-5-methylolundecane.

The ester was evaluated as an extractant for copper from aqueoussolution containing chloride ion, using the method of Example 7.

The results are displayed in Table 3, and indicate that the extractantis more suitable for use with leach solutions having relatively lowtotal chloride ion concentrations (3.7M), since relatively high acidtransfer levels occur at high total chloride ion concentrations (9.8M).

EXAMPLE 9

(2-(n)Hexyldecyl)picolinate was prepared from picolinic acid and2-(n)hexyldecyl alcohol by the general method of Example 1 with thefollowing differences. The temperature after thionyl chloride additionwas maintained at 80° C. for 2 hours and after the esterificationreaction, the solution was diluted with petroleum ether 60°-80°, washedwith 1M hydrochloric acid and with brine (10 % NaCl). The solvents wereremoved by evaporation and the dark coloured oil distilled (boilingrange 176°-178° C. at 0.07 mm mercury pressure) to give a colourless oilof estimated purity 97.5%.

The ester was evaluated as an extractant for copper from aqueoussolutions containing chloride ions by the general method of Examples 6and 7, except that AROMASOL H was used as solvent. The solution Acontained the higher levels of chloride ion (9.8M) indicated in Example7 and Table 3. Table 3 shows that the extractant is comparatively wellsuited for operation using leach solutions containing higher levels oftotal chloride ion since only 9% transfer of hydrochloric acid tookplace at a total chloride ion concentration of 9.8M.

EXAMPLE 10

Isooctadecyl picolinate was prepared using the method of Example 7 frompicolinic acid and isooctadecyl alcohol, the commercial materialobtained from Fabwerke Hoechst AG and described in Example 8. The lightbrown, oily product of the reaction had an estimated purity of 93.5%.

The ester was evaluated as an extractant for copper from aqueoussolutions containing chloride ion using the method of Example 7, exceptthat AROMASOL H was used as solvent.

The results are displayed in Table 3, and show that whilst a relativelylow extraction of copper takes place from 3.7M total chloride ionsolution, good extraction of copper with relatively low acid transfertakes place from 9.8M total chloride ion solution.

EXAMPLE 11

The bis isodecyl ester of pyridine-3,5-dicarboxylic acid was prepared bythe method of Example 1 from pyridine-3,5-dicarboxylic acid andcommercial isodecanol (obtained from ICI Petrochemicals Division) usingmodified amounts of reactants as required by the stoichiometry. Toluenewas used as reaction solvent in place of xylene and the temperature wasmaintained at 80°-82° C. for 4 hours after the thionyl chlorideaddition. Following the esterification reaction, the solution wascooled, washed with dilute sodium hydroxide solution, 1M hydrochloricacid, 0.5M hydrochloric acid and water. The solution was treated withactivated carbon (8% on the expected weight of product), the solventevaporated at reduced pressure and the residue distilled (boiling range200°-210° C. at 0.08 mm mercury pressure) to give a product having aestimated purity of 97.5%.

This bis-ester was evaluated as an extractant for copper from aqueoussolutions containing chloride ion by the method of Examples 6 and 7.

To evaluate the efficiency of the extractant for use with leachsolutions containing both high levels of total chloride ion and highacid levels, the general test method of Examples 6 and 7 was repeatedusing a solution A which contained cupric chloride (0.1M), hydrochloricacid (1.0M) and calcium chloride dihydrate (700 g/l), giving a totalchloride ion concentration of 10.7M.

The results are displayed in Table 3, and show that whilst a relativelylow extraction of copper takes place from 3.7M total chloride ionsolution, excellent extraction of copper takes place with no acidtransfer from solutions containing a total chloride ion concentration of9.8M, and low acid transfer levels are achieved even when the totalchloride ion concentration is 10.7M.

EXAMPLE 12

The bis nonyl ester of pyridine-2,4-dicarboxylic acid was prepared usingthe method of Example 1 from pyridine-2,4-dicarboxylic acid andcommercial nonanol (obtained from ICI Petrochemicals Division andcontaining predominantly 3,5,5-trimethylhexanol), with modified amountsof reactants as required by the stoichiometry. After the thionylchloride addition, the temperature was maintained at 84°-85° C. for 2hours whilst after the esterification reaction the product was isolatedas described in Example 7. The boiling range of the product was200°-210° C. at 0.2 mm mercury pressure and the estimated purity was100%.

The bis-ester was evaluated as an extractant for copper from aqueoussolutions containing chloride by the method of Examples 6 and 11, exceptthat AROMASOL H was used as solvent.

The results are shown in Table 3.

EXAMPLE 13

The bis-isodecyl ester of pyridine 2,5-dicarboxylic acid was preparedusing the method of Example 1 from pyridine-2,5-dicarboxylic acid andcommercial isodecanol, obtained from ICI Petrochemicals Division, withmodified amounts of reactants as required by the stoichiometry. Toluenewas used as solvent for the reaction, in place of xylene, and after thethionyl chloride addition the temperature was maintained at 77°-83° C.for 11/2 hours. After the esterification reaction the product wasisolated as described in Example 7, and had a boiling range of 219°-221°C. at 0.08 mm mercury pressure, and estimated purity of 95.5%.

The bis-ester was evaluated as an extractant for copper from solutionscontaining chloride by the method of Examples 7 and 11.

The results are displayed in Table 3.

EXAMPLE 14

N,N-Di-(n)-octyl picolinamide was prepared using the method of Example 1from picolinic acid and di-(n)-octylamine. After the addition of thionylchloride, the temperature was maintained at 79°-80° C. for 5 hours andthen raised to distil excess thionyl chloride and a little xylene. Theacid chloride suspension was cooled to 48° C. and the molten amine wasadded at 48°-74° C. over 10 minutes. The reaction was contained at 90°C. for 4 hours and the dark brown solution was cooled and washed withwater to remove acidity. The solution was treated with activated carbon(10% on the expected weight of product), filtered, the solventevaporated and the dark brown oil distilled. The product had a boilingrange of 175°-180° C. at 0.15 mm mercury pressure and was dark coloured.It was purified by dissolving in toluene, treating with activated carbon(10% on expected weight of product) and extracting with 2M sodiumhydroxide and water. The toluene was removed by evaporation underreduced pressure to give a mid-brown coloured oil of estimated purity91%.

The amide was evaluated as an extractant for copper from solutionscontaining chloride ion as in Examples 6 and 7, except that AROMASOL Hwas used as solvent.

The results are displayed in Table 3.

                  TABLE 3                                                         ______________________________________                                        Transfer of copper (%) and hydrochloric acid                                  (%) from aqueous solution                                                            SOLUTION COMPOSITION                                                          HCl 0.1 M          HCl 1.0 M                                                    Calcium     Calcium     Calcium                                               chloride    chloride    chloride                                              250 g/l     700 g/l     700 g/l                                      Extractant                                                                             Total chloride                                                                            Total chloride                                                                            Total chloride                               (Example 3.7 M       9.8 M       10.7                                         No.)     Cu      H       Cu    H     Cu    H                                  ______________________________________                                        6        52      0                                                            7        54      0       77    25                                             8        49      0       74    25                                              9*                      73    9                                              10*      20      0       68    7                                              11       22      0       80    0     79    6                                  12*                      52    0     51    4                                  13                       17    0     29    8                                  14*                      66    21                                             25*                      23    3                                              26*      66      12      89    22                                             ______________________________________                                         ESCAID 100 was used as solvent except for those Examples marked * where       the solvent was AROMASOL H.                                              

EXAMPLE 15

A 0.5 molar solution of te extractant of Example 1 in Aromasol H (20 ml)was shaken for 1 minute with an equal volume of a solution containing37.6 g/l zinc, 3.65 g/l HCl and 65 g/l calcium (all as chlorides) havinga total chloride ion concentration of 4.5 molar.

Analysis of the resulting aqueous phase showed that it contained 28.1g/l zinc, indicating a zinc transfer of 25.3%.

EXAMPLE 16

The solvent extraction circuit described in Example 5 was used toevaluate the extractant of Example 1. The feed was:

    ______________________________________                                        Copper (Cu.sup.2+)                                                                             25           g/l                                             Iron (Fe.sup.2+) 75           g/l                                             Silver (Ag.sup.+)                                                                              0.028        g/l                                             Lead (Pb.sup.2+) 1.5          g/l                                             Arsenic (As.sup.3+)                                                                            0.2          g/l                                             Antimony (Sb.sup.3+)                                                                           0.10         g/l                                             Mercury (Hg.sup.+)                                                                             0.005        g/l                                             ______________________________________                                    

With the exception of silver, which was added as silver nitrate tofacilitate dissolution, the metals were in the form of their chlorides.In addition, the solution contained 1.8 g/l of hydrogen chloride, givinga total chloride ion concentration of 3.5 moles per liter.

The strip solution consisted of an aqueous solution containing 29 g/lcopper as cupric chloride, adjusted to pH 1.0 with hydrochloric acid.

The solvent phase comprised 175 g/l (0.5M) of the extractant of Example1 dissolved in AROMASOL H.

The operating conditions were as described in Example 5, except that theaqueous feed to the first strip mixer-settler was heated, and thestripped organic phase returned to the extraction mixer-settlers wascooled. As a result, the first strip stage operated at an averagetemperature of 45° C., whilst the second strip stage operated at anaverage temperature of 34° C. The extraction stages operated at 28° C.

The circuit was operated for 53.5 hours with steady transfer of copperfrom the aqueous feed solution to the strip solution throughout theperiod of operation as indicated by analysis of solutions passingthrough the circuit at the times listed below:

    ______________________________________                                        Time  Cu.sup.2+ g/l                                                           (hours)                                                                             Raffinates                                                                              Stripped Organic                                                                            Pregnant Strip Soln.                            ______________________________________                                        12    8         12            45                                              40    10         9            49                                              45    9         10            43                                              53.5  8         10            41                                              ______________________________________                                    

During the period of operation, analysis for the minor metals present inthe feed gave the following results (g/l):

    ______________________________________                                                  Ag.sup.+                                                                             Pb.sup.2+                                                                            As.sup.3+                                                                              Sb.sup.3+                                                                          Hg.sup.+                                ______________________________________                                        Strip solution                                                                            0.001    0.015  0.004  0.010                                                                              0.0002                                Pregnant strip                                                                            0.001    0.030  0.008  0.012                                                                              0.0002                                solution                                                                      ______________________________________                                    

By way of comparison, the circuit was operated under identicalconditions, except that no heating of the strip circuit was used, andall mixer-settlers operated at ambient temperature (22° C.). Noprecipitate was observed but a gradual build-up of an oligomeric coppercomplex species was inferred from copper loadings on the extractantgreater than that expected for the species L₂ CuCl₂, where L representsthe extractant. The circuit was operated for 30 hours, and during thisperiod, the concentration of copper in both the raffinate and thestripped organic phase steadily increased as indicated below:

    ______________________________________                                                                  Stripped organic                                    Time (hours)                                                                             Raffinate (Cu.sup.2+ g/l)                                                                    (Cu.sup.2+ g/l)                                     ______________________________________                                        10         10.5           11.4                                                20         13.4           13.3                                                30         15.2           15.0                                                ______________________________________                                    

EXAMPLE 17

The nicotinic acid ester of 2,2,4,8,10,10-hexamethyl-5-methylolundecane(the latter being derivable from the self condensation of two moleculesof ##STR9## via the Guerbet reaction) was prepared using the method ofExample 1. The product had a boiling point of 145° to 150° C. at 0.1 mmpressure and an estimated purity of 90.8%.

The ester was evaluated as an extractant for copper from aqueoussolution containing chloride ion using the method of Example 1.

The results are as follows:

    ______________________________________                                                               %                                                      ______________________________________                                        Transfer of copper from 0.1 M HCl to B                                                                 42.5                                                 Transfer of copper from 0.1 M HCl to C                                                                 23.6                                                 Transfer of copper from 1.0 M HCl to B                                                                 48.0                                                 Transfer of copper from 1.0 M HCl to C                                                                 30.2                                                 Acid co-extracted from 1.0 M HCl to B                                                                   2.6                                                 ______________________________________                                    

The acid co-extracted from 0.1M HCL to B was negligible.

EXAMPLES 18 TO 24

The effect of different ester groups on the solubility of aligand-copper^(II) chloride complex in concentrated solution in anon-polar solvent was examined as follows: Pyridine 3,5-dicarboxylicacid bis esters were prepared by esterifying pyridine 3,5-dicarboxylicacid with a series of different alcohols according to the procedure ofExample 11 (see Table 4). Each ester in turn was made up as a 0.5Msolution in ESCAID 100 and loaded with copper^(II) chloride (toapproximately 75% of the theoretical amount according to thestoichiometry of L₂ CuCl₂ where L is the bis ester) by shaking withtwice its volume of an aqueous solution which was 0.1M in HCl, 0.4M inCuCl₂ and which in addition contained 250 g/l of calcium chloridedihydrate. Any separation of the metal ligand complex from the organicsolution was noted (Test 1). If no separation occurred, the organicsolvent was loaded to approximately 100% of theoretical by shaking witha second aqueous solution which differed from the first only incontaining 500 g/l of calcium chloride dihydrate. Again any separationof complex from the organic solution was noted (Test 2). Results arelisted below in Table 4.

                  TABLE 4                                                         ______________________________________                                        Example                                                                              Alcohol used    Test 1     Test 2                                      ______________________________________                                        18     Mixed isomer    Immediate  --                                                 iso-octanol     precipitation                                                                 occurred                                               19     2-ethylhexanol  Immediate  --                                                                 precipitation                                                                 occurred                                               20     Commercial nonanol                                                                            Immediate  --                                                 (3,5,5-trimethyl-                                                                             precipitation                                                 hexanol)        occurred                                               21     Diisobutyl      No         Precipitation                                      carbinol        precipitation                                                                            occurred                                                                      after 2 weeks                               22     Mixed isomer    No         No                                                 isononanol*     precipitation                                                                            precipitation                                                                 after 2 weeks                               23     Mixed isomer    No         No                                                 isodecanol      precipitation                                                                            precipitation                                                                 after 2 weeks                               24     Mixed isomer    Some       --                                                 tridecanol      precipitation                                                                 occurred but                                                                  only after                                                                    2 weeks                                                ______________________________________                                         *The mixed isomer isononanol was obtained by hydroformylation of a mixed      octene stream.                                                           

The results indicate that the bis esters of Examples 18, 19, 20, 21 and24 would require to be used in more dilute solution or in a more polarsolvent than EXCAID 100, for example a solvent having a higher aromaticcontent, but that the bis esters of Examples 22 and 23 and their coppercomplexes have excellent solubility even in concentrated solution in avery weakly polar solvent of low aromatic content.

EXAMPLE 25

N,N,N',N'-tetraisoamyl pyridine-2,5-dicarboxamide was prepared using themethod of Example 1 from pyridine-2,5-dicarboxylic acid anddiisoamylamine. The crude product in toluene solution was washed severaltimes with 0.5M aqueous sodium hydroxide and then with 0.5M aqueoushydrochloric acid and water. The solution was then treated with charcoaland filtered. The solvent was distilled under reduced pressre, but theproduct, a brown oil, was not itself distilled. It was made up as a 0.2Msolution in AROMASOL H and tested for extraction of copper in thepresence of chloride ion using the method of Examples 6 and 7 exceptthat AROMASOL H was used as solvent. The results are given in Table 3.The results indicate that this is a very weak extractant suitable forrecovering copper from aqueous solution of high chloride ionconcentrations.

EXAMPLE 26

3-hexylundecylamine was prepared from 2-hexyldecanol as follows. Thealcohol was heated to 96°-107° and stirred whilst a stream of hydrogenbromide gas was bubbled through it for 4 hours. The organic layer wasseparated, and washed first with 96% sulphuric acid and then with water,aqueous ammonia until neutral, and water, and then distilled yielding1-bromo-2-hexyldecane (b.p. 140° at 1 mm pressure). The bromo compoundwas converted to 1-cyano-2-hexyldecane by stirring it at the refluxtemperature with excess of a 44% aqueous solution of sodium cyanide, inthe presence of methyl trioctyl ammonium chloride as a phase transfercatalyst, following C. M. Starks (Journal of the American ChemicalSociety, 93, page 195, 1971). After washing with dilute aqueous sodiumhydroxide solution and water, the cyano compound (141 grams) wasdissolved in ethanol (130 ml) and poured into an autoclave. Liquidammonia (150 g) was added and the autoclave was pressurised to 50atmospheres with hydrogen, sealed, and heated to 170° for 24 hours. Theautoclave was cooled, and most of the ammonia allowed to evaporate. Thesolution was filtered and the solvent was distilled under reducedpressure. It was found by gas chromatography that complete conversion to3-hexylundecylamine had taken place.

N,N'-bis(3-hexylundecyl)pyridine-2,5-dicarboxamide was prepared usingthe method of Example 1 from 3-hexylundecylamine and pyridine2,5-dicarboxylic acid. The product which was a brown oil was notdistilled but was analysed as being 92% of theoretical strength (basedon MW 642) by titration of an aliquot in acetic acid with perchloricacid. It was made up as a 0.2M solution in AROMASOL H and tested forextraction of copper in the presence of chloride ion using the method ofExamples 6 and 7. The results are given in Table 3. They indicated thatthis compound is a strong extractant for copper which would be bestemployed in extracting copper from solutions of relatively low chlorideion concentration and relatively low acidity.

EXAMPLE 27

Isohexadecyl-5-bromonicotinate was prepared from 5-bromo nicotinic acidand commercial iso-octadecyl alcohol using the general method of Example8, except that toluene was used as the solvent in place of xylene. Thusisohexadecyl-5-bromonicotinate (101 parts) was suspended in toluene (240parts) and dimethyl formamide (1.01 parts) and the suspension stirredand heated to 70° to 80° C. Thionyl chloride (65.45 parts) was addeddropwise to the above suspension over about 30 minutes which was thenstirred and heated at 70° to 80° C. for a further hour. Excess thionylchloride was removed by distillation, which also removed a proportion ofthe toluene. Commercial hexyldecanol (121 parts) was added to theresultant solution over a period of about 30 minutes and the mixture washeated at 70° to 80° C. for a further two hours. The product wasisolated by cooling the toluene solution to ambient temperature followedby water washing and distillation to yield 201.4 parts ofisohexadecyl-5-bromonicotinate, which had a boiling range of 165° to175° C. at 0.1 mm mercury pressure.

The ester was evaluated as an extractant for copper as a 0.2 molarsolution in SOLVESSO 150, a commercial hydrocarbon solvent of higharomatic content, using the method of Examples 6 and 11. The results aredisplayed in Table 5, wherein the headings correspond to those of Table3.

                  TABLE 5                                                         ______________________________________                                        Transfer of copper (%) and hydrochloric acid                                  (%) from aqueous solution                                                            SOLUTION COMPOSITION                                                          HCl 0.1 M         HCl 1.0 M                                                     Calcium     Calcium     Calcium                                               chloride    chloride    chloride                                              250 g/l     700 g/l     700 g/l                                      Extractant                                                                             Total chloride                                                                            Total chloride                                                                            Total chloride                               (Example 3.7 M       9.8 M       10.7 M                                       No.)     Cu      H       Cu    H     Cu    H                                  ______________________________________                                        27       --      --      39    0     48    6                                  ______________________________________                                    

We claim:
 1. A substituted pyridine which has the formula: ##STR10##wherein R₁ is a hydrocarbyl group containing from 5 to 36 carbon atoms,the two groups R₁ may be the same or different and the two groups R₁together contain a total of from 16 to 36 carbon atoms.
 2. A substitutedpyridine according to claim 1 in which R₁ is a mixture of octyl groupsderived from mixed isomer iso-octanol.
 3. A substituted pyridine as setforth in claim 1 in which R₁ is 2-ethyl hexyl.
 4. A substituted pyridineas set forth in claim 1 in which R₁ is 3,5,5-trimethyl hexyl.
 5. Asubstituted pyridine as set forth in claim 1 in which R₁ isdiisobutylmethyl.
 6. A substituted pyridine as set forth in claim 1 inwhich R₁ is a mixture of nonyl isomers derived from mixed isomerisononanol.
 7. A substituted pyridine as set forth in claim 1 in whichR₁ is a mixture of decyl isomers derived from mixed isomer isodecanol.8. A substituted pyridine as set forth in claim 1 in which R₁ is amixture of tridecyl isomers derived from mixed isomer tridecanol.